An improved magnetic pump is disclosed. More specifically, a magnetic pump is disclosed that includes a brushless DC motor which comprises a magnetic carrier mounted to the drive shaft which carries at least six bar magnets. The drive shaft and carrier pass through a DC stator coil. At least six sensor magnets are used which transmit signals to a Hall effect sensor which, in turn, transmits feedback signals to a controller for an improved speed control.
Gear pumps are conventionally housed in sealed enclosures from which the pump shaft extends. A drive motor is coupled to the shaft to rotate the shaft and pump rotor.
Typically, such xe2x80x9cdirect drivexe2x80x9d pumps include dynamic bearing seals through which the drive shaft passes to prevent fluid leaks into the motor casing. The use of such dynamic bearing seals presents a number of problems. For example, the seals are exposed to constant frictional forces and, therefore, require maintenance to provide a leak-free environment for the motor. Further, excessive frictional loading by the seals on the pump shaft decreases pump efficiency and results in heat generation. These factors decrease pump reliability, pump lifetime and contribute to seal failure which can cause the motor to be exposed to the liquid being pumped.
To eliminate these problems, magnetic drive systems have been employed which eliminate the need for the drive shaft to pass through the pump the exterior of the pump enclosure. Such magnetic pumps are disclosed in U.S. Pat. Nos. 3,238,883, 4,111,614, 5,096,390 and 5,197,865.
The ""883 and ""614 patents disclose the use of brushed motors whereby electrically conductive brushes are spring biased against the rotor shaft to make electrical connections with the winding mounted onto the motor shaft. Due to their reliance upon an electro-mechanical contact against a moving element, the motor brushes are prone to intermittent contacts and ultimate failure.
To solve this problem, the ""390 and ""865 patents incorporate a brushless DC (BLDC) motor which utilize a stationary rotor coil through which the drive shaft passes. Circular magnets are mounted onto the drive shaft.
However, the use of circular magnets provides relatively poor speed control. In an attempt to overcome this problem, the ""390 and ""865 patents utilize a specially designed circuit board to control the operation of the pump. Because the pumps are intended to be used for a variety of purposes, the circuit boards must often be customized.
As a result, there is a need for an improved BLDC pump with improved speed control and with standardized electrical components that can be directly coupled to a controller. Such improved control would be important for metering applications with a positive displacement pump whereby variable loads are imposed on the pump due to changes in input and discharge pressure which can alter flowrate.
In satisfaction of the aforenoted needs, a brushless direct current magnetic pump is provided that comprises a drive shaft that passes through and that is coupled to a magnet carrier. The magnetic carrier comprises an annular sleeve comprising an inner surface that engages the drive shaft and extends along a portion of the drive shaft. The sleeve further comprises an outer surface comprising at least six circumferentially spaced apart elongated ribs that extend axially along the outer surface of the sleeve. The sleeve further includes at least six elongated slots with each slot being disposed between two of the ribs. The pump also comprises at least six bar magnets with each bar magnet being accommodated in one of the slots so that the bar magnets are also circumferentially spaced around the outer surface of the annular sleeve. The pump also comprises at least six sensor magnets with each sensor magnet being accommodated in one of the slots so that the six sensor magnets are also circumferentially spaced around the outer surface of the annular sleeve. Each sensor magnet is also axially spaced apart from one of the bar magnets. Accordingly, each groove of the annular sleeve accommodates a bar magnet and a sensor magnet with the space therebetween. The sensor magnets are coupled to a Hall effect sensor for monitoring the speed and operation of the pump.
In a refinement of the above concept, the pump comprises eight bar magnets and eight sensor magnets and, therefore, the sleeve comprises eight ribs and eight slots.
In a further refinement, the Hall effect sensor is linked to a controller for controlling and monitoring the speed and operation of a pump.
In yet a further refinement, an improved system for manufacturing foam is provided which includes at least two pumps as described above. One of the pumps has an inlet that is connected to a supply of a first reagent. The other of the pumps has an inlet that is connected to a supply of a second reagent. Each of the pumps has an outlet that is connected to the Hall effect sensors of each of the pumps are linked to a common controller for controlling the operation and the speed of the two or more pumps.